Various types of probe support devices have heretofore been provided for effecting scanning movements of probes, for the inspection of inside surface portions of pipes or tubes or parts having bolt holes or the like through which fastening elements are extended. The Drummond et al U.S. Pat. No. 2,308,159 and also the Hastings et al U.S. Pat. No. 2,684,464 disclose devices in which a test coil structure is supported on a spindle which is operated through drive and gearing means for simultaneous rotational and axial movement of the test coil structure to trace a helical path within a tube or the like. Slip rings are used for transmission of electrical signals.
The Rogel et al U.S. Pat. No. 3,718,855 provides another disclosure of a device for moving the probe in a helical path, using drive and gearing means similar to the drive and gearing means of the Drummond et al and Hastings et al patents but differing therefrom in using a universal mounting bracket and a housing removably secured thereto.
Another arrangement is disclosed in the Scalese et al U.S. Pat. No. 3,831,084, also operative to effect a helical scan, but using a solenoid-operated plunger for selective control of rotation of a sleeve of the assembly. The Scalese et al patent shows limit switches used in a conventional manner to change the direction of movement or to stop rotation at limits of travel.
Such prior art types of probe support devices have been advantageously used to move an eddy current probe within a bolt hole. With an eddy current probe and with associated electronic instrumentation, as heretofore developed, the probes may be of very small size and it is possible to obtain highly accurate and reliable information as to the condition of the surface portion of a part around a bolt hole or the like, particularly with respect to the detection of cracks or other defects which might lead to failure of the part. Such information is extremely important in the testing of critical parts such as certain aircraft parts, for example.
For such applications, probe support devices of the prior art have been generally satisfactory, especially when carefully used. However, under certain conditions of use, they have been subject to malfunctions. When such have been detected, it has generally been the practice immediately to send the device to a shop having the necessary repair facilities and personnel to have the device repaired and to permit the testing operation to continue as promptly as possible. In such cases, valuable time may be lost. In other cases, malfunctions have escaped oftentimes to compromise the integrity of the testing operation.